In the manufacture of some types of printed wiring boards, an insulation substrate, which may be rigid or flexible, is typically formed with copper cladding on one or both major surfaces thereof. Conventional techniques, such as imaging, plating, etching and drilling, are then employed to selectively form circuit patterns on the copper cladding. Circuit patterns of varying complexity and density may be formed in this manner. Typically, simple low density circuit patterns may be formed on substrates having copper only on one major surface by drilling, imaging and etching. Plating may also be employed for suitable finishing to enhance solderability or to add precious metal contact areas for interconnecting to other circuits. Complex circuits may be formed on the substrate having copper on both major surfaces using a substractive process. Typically, holes, which are formed in the substrate by drilling, punching or a laser, are subsequently plated to interconnect conductive circuit patterns on one major surface of the substrate to circuit patterns formed on the opposite major surface of the substrate. If a higher density of circuits is required, patterned substrates may be stacked and laminated together to form multilayered printed circuits. As noted above, circuit patterns on the various layers are interconnected with plated-through holes, which are typically formed along with surface layer circuit patterns or pads after the lamination operation.
In either type of manufacture of printed circuits, the base for the printed circuit is the substrate. In some instances, the substrate is formed by woven or random matted fibers, such as glass or polyester, which are impregnated in a suitable resin to impart physical and electrical properties to the substrate. The substrate may be comprised of single or multiple layers of reinforcement depending on the desired thickness and physical properties. In other instances, the substrate is composed of a special material, or specially treated material, which permits the direct circuit-pattern application of copper to the substrate. A system of this type is disclosed in U.S. Pat. No. 4,077,927 which issued to C. A. McPherson on Mar. 7, 1978.
In still another type of substrate, a metal panel is coated with an epoxy resin following the formation of a suitable hole pattern. Copper is selectively plated onto the epoxy resin surface and through the holes by additive techniques to form the desired circuit pattern. A metal panel substrate of this type, and the technique for making the substrate is disclosed in an article entitled "An Insulated Metal Printed Wire Board" authored by Donald Dinella and appears at pages 24 through 29 in the Western Electric Engineer, Volume 9, No. 3, dated July 1965. Typically, the metal panel is composed of a steel alloy which provides an electrostatic and magnetic shield. Further, the presence of the metal panel provides heat dissipation for components subsequently secured to the panel and connected to circuits formed thereon.
Although the metal panel substrate possesses the properties of strength, heat dissipation and shielding, there are instances when it would be desirable to use a metal coated non-metallic substrate having the same properties as the resin-coated metal panel but which is manufactured by use of conventional techniques.
Consequently, there is a need for a substrate or laminate having the advantages of strength, shielding and heat dissipation which is manufactured utilizing existing conventional printed wiring board technology which will provide for high density printed wiring and maximum economies of manufacture.